To facilitate provision of atovaquone (566C80) to patients who have mild to moderate Pneumocystis carinii pneumonia (PCP) and are intolerant and/or unresponsive to trimethoprim / sulfamethoxazole (TMP / SMX ); to monitor serious adverse events attributable to 566C80.

Inclusion Criteria

Patients must have the following:

• Clinical diagnosis of acute mild to moderate Pneumocystis carinii pneumonia.
• Dose-limiting intolerance to TMP / SMX or inadequate response to TMP / SMX.
• Willingness and ability to give informed consent. The clinical condition of the patient and appropriate physiologic criteria should be used in evaluating patients for therapy with 566C80. Patients who are rapidly progressing in disease severity or have severe disease as evidenced by sustained tachypnea (e.g., sustained respiratory rate > 30 breaths/minute), rapid deterioration in (A-a)DO2 and chest radiograph may not be appropriate candidates for oral therapy, including 566C80. Therapy with parenteral pentamidine should be undertaken in these cases. Treatment with IV trimetrexate or primaquine / clindamycin should be considered for these patients unless the patient is known to have dose-limiting intolerance to these agents. Patients with severe PCP who are intolerant and/or unresponsive to therapy with TMP / SMX and parenteral pentamidine may enroll in the 566C80 open-label compassionate plea protocol.

Exclusion Criteria

Patients with the following prior conditions are excluded: History of serious or dose-limiting adverse experience during previous 566C80 therapy, thought to be attributable to the drug.